This invention relates to a process for pickling electrical steel. More particularly, this invention relates to a method for pickling silicon-containing electrical steel strip using hydrogen peroxide.
Silicon-containing electrical steels are low carbon (from about 0.1% or less) specialty steels typically containing from about 0.5% to about 3.5% silicon. These steels include grain oriented and non-oriented steels. Hot processing of silicon-containing electrical steels can result in the formation of oxides on the surface of the steel strip. These oxides are primarily comprised of iron, silicon, and other associated metals, which must be removed prior to cold reduction and other subsequent processing. Traditionally, these oxides have been removed by an initial mechanical treatment such as shot blasting, which is followed by a chemical treatment such as pickling with nitric acid, or, nitric acid in combination with hydrochloric acid and hydrofluoric acid.
There is a desire for a method of pickling electrical steels that eliminates the use of nitric acid.
The present invention relates to a process for pickling silicon-containing electrical steel strip. The pickling process comprises of plurality of pickling tanks containing hydrochloric and hydrofluoric acids along with hydrogen peroxide sprayers located between the pickling tank treatments. The sprayers are located above the solution contained in the pickling tanks and the spray solution comprises an aqueous solution of hydrogen peroxide. The process comprises of continuous multiple treatments of immersing the steel strip in a pickling tank and then spraying the top and bottom surfaces of the steel strip with the spray solution as it exits the pickle tank and before it enters the next pickle tank. Upon exiting the last pickling tank, the strip is brushed/scrubbed.
This process may also comprise of a single pickling tank containing hydrochloric and hydrofluoric acids along with the hydrogen peroxide sprayers located the strip entry in to the pickling tank. The sprayers are located above the solution contained in the pickling tank and the spray solution comprises an aqueous solution of hydrogen peroxide or an acidified aqueous solution of hydrogen peroxide.